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Trailing suction hopper dredger contains a large hopper for storage and transport of dredged materials. The dredging operation is implemented by a hydraulic dredging system including draghead, suction pip, pumps for taking up the material from seabed and putting them into the hopper.
Vertical drains are commonly installed in square and triangular patterns. The zone of influence of vertical drains (R) is a function of drain spacing (S).
For drains in square pattern: R = 0.546S
For drains in triangular pattern: R = 0.525S
Shoes are normally installed in prefabricated drains for the following reasons:
(i) It avoids the entry of soils into the mandrel by sealing it during the installation of drains.
(ii) It performs like an anchor to retain the drains at the designed depth and to stop the drains from being pulled out during the withdrawn of mandrels after driving the mandrels into ground.
For installation of band drains by marine plants, it must have sufficient water depth to accommodate the marine plants in the first place. However, due to the effect of tides and waves, the establishment of the position for installation of band drains and the subsequent installation works may be affected. In addition, the establishment cost of marine plants is higher than that of land plants.
During installation of band drains, smear zones are created in which a zone of soil surrounding the band drains are disturbed. The compressibility of surrounding soils is increased and it results in the reduction of their permeability.
